diff --git a/ChangeLog b/ChangeLog index 6f08b20bd..aac45a472 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,13 @@ +2019-02-02 Nikolaus Waxweiler + + [sfnt] Use typo metrics if OS/2 fsSelection USE_TYPO_METRICS bit is set. + + If the OS/2 table exists and fsSelection bit 7 (USE_TYPO_METRICS) is set, + use the sTypo* set of values to compute the FT_Face's ascender, descender + and height. Otherwise, fall back to old behavior. + + * src/sfnt/sfobjs.c (sfnt_load_face): Implement. + 2019-01-18 John Tytgat [sfnt] Handle TT fonts having two PostScript font names (#55471). @@ -420,7 +430,7 @@ * src/base/ftobjs.c (ft_glyphslot_preset_bimap): Another tweak. This one should be clearer. When the rounded monochrome bbox collapses - we add a pixel that covers most if not all original cbox. + we add a pixel that covers most if not all original cbox. 2018-09-21 Alexei Podtelezhnikov diff --git a/src/sfnt/sfobjs.c b/src/sfnt/sfobjs.c index 7705c08ae..126e174d7 100644 --- a/src/sfnt/sfobjs.c +++ b/src/sfnt/sfobjs.c @@ -1641,59 +1641,73 @@ root->units_per_EM = face->header.Units_Per_EM; - /* XXX: Computing the ascender/descender/height is very different */ - /* from what the specification tells you. Apparently, we */ - /* must be careful because */ - /* */ - /* - not all fonts have an OS/2 table; in this case, we take */ - /* the values in the horizontal header. However, these */ - /* values very often are not reliable. */ - /* */ - /* - otherwise, the correct typographic values are in the */ - /* sTypoAscender, sTypoDescender & sTypoLineGap fields. */ - /* */ - /* However, certain fonts have these fields set to 0. */ - /* Rather, they have usWinAscent & usWinDescent correctly */ - /* set (but with different values). */ - /* */ - /* As an example, Arial Narrow is implemented through four */ - /* files ARIALN.TTF, ARIALNI.TTF, ARIALNB.TTF & ARIALNBI.TTF */ - /* */ - /* Strangely, all fonts have the same values in their */ - /* sTypoXXX fields, except ARIALNB which sets them to 0. */ - /* */ - /* On the other hand, they all have different */ - /* usWinAscent/Descent values -- as a conclusion, the OS/2 */ - /* table cannot be used to compute the text height reliably! */ - /* */ + /* + * Computing the ascender/descender/height is tricky. + * + * The OpenType specification v1.8.3 says: + * + * [OS/2's] sTypoAscender, sTypoDescender and sTypoLineGap fields + * are intended to allow applications to lay out documents in a + * typographically-correct and portable fashion. + * + * This is somewhat at odds with the decades of backwards + * compatibility, operating systems and applications doing whatever + * they want, not to mention broken fonts. + * + * Not all fonts have an OS/2 table; in this case, we take the values + * in the horizontal header, although there is nothing stopping the + * values from being unreliable. Even with a OS/2 table, certain fonts + * set the sTypoAscender, sTypoDescender and sTypoLineGap fields to 0 + * and instead correctly set usWinAscent and usWinDescent. + * + * As an example, Arial Narrow is shipped as four files ARIALN.TTF, + * ARIALNI.TTF, ARIALNB.TTF and ARIALNBI.TTF. Strangely, all fonts have + * the same values in their sTypo* fields, except ARIALNB.ttf which + * sets them to 0. All of them have different usWinAscent/Descent + * values. The OS/2 table therefore cannot be trusted for computing the + * text height reliably. + * + * As a compromise, do the following: + * + * 1. If the OS/2 table exists and the fsSelection bit 7 is set + * (USE_TYPO_METRICS), trust the font and use the sTypo* metrics. + * 2. Otherwise, use the `hhea' table's metrics. + * 3. If they are zero and the OS/2 table exists, + * 1. use the OS/2 table's sTypo* metrics if they are non-zero. + * 2. Otherwise, use the OS/2 table's usWin* metrics. + */ - /* The ascender and descender are taken from the `hhea' table. */ - /* If zero, they are taken from the `OS/2' table. */ - - root->ascender = face->horizontal.Ascender; - root->descender = face->horizontal.Descender; - - root->height = root->ascender - root->descender + - face->horizontal.Line_Gap; - - if ( !( root->ascender || root->descender ) ) + if ( face->os2.version != 0xFFFFU && face->os2.fsSelection & 128 ) { - if ( face->os2.version != 0xFFFFU ) + root->ascender = face->os2.sTypoAscender; + root->descender = face->os2.sTypoDescender; + root->height = root->ascender - root->descender + + face->os2.sTypoLineGap; + } + else + { + root->ascender = face->horizontal.Ascender; + root->descender = face->horizontal.Descender; + root->height = root->ascender - root->descender + + face->horizontal.Line_Gap; + + if ( !( root->ascender || root->descender ) ) { - if ( face->os2.sTypoAscender || face->os2.sTypoDescender ) + if ( face->os2.version != 0xFFFFU ) { - root->ascender = face->os2.sTypoAscender; - root->descender = face->os2.sTypoDescender; - - root->height = root->ascender - root->descender + - face->os2.sTypoLineGap; - } - else - { - root->ascender = (FT_Short)face->os2.usWinAscent; - root->descender = -(FT_Short)face->os2.usWinDescent; - - root->height = root->ascender - root->descender; + if ( face->os2.sTypoAscender || face->os2.sTypoDescender ) + { + root->ascender = face->os2.sTypoAscender; + root->descender = face->os2.sTypoDescender; + root->height = root->ascender - root->descender + + face->os2.sTypoLineGap; + } + else + { + root->ascender = (FT_Short)face->os2.usWinAscent; + root->descender = -(FT_Short)face->os2.usWinDescent; + root->height = root->ascender - root->descender; + } } } }